Metamaterials are artificial materials that allow light to be to controlled and manipulated with precision. Metamaterials are materials that include periodic or non-periodic distributions of meta-atoms. They inherit their properties from the structures of the meta-atoms, rather than from the materials of which they are made. Typically, metamaterials are made by periodic arrangements of metallic nanofeatures, but more recently they have been realized with all-dielectric materials.
Metamaterials are “effective media”, because the meta-atoms are typically smaller than the wavelength at which they operate. Thus, the media can be effectively considered homogeneous. Importantly, metamaterials allow the effective permittivity and permeability, and so the refractive index, to be specified locally, with high spatial accuracy.
Metamaterials have been known for some time. Examples of metamaterials that are effective in the visible range are described by Enkrich et al in “Magnetic Metamaterials at Telecommunication and Visible Frequencies” PHYSICAL REVIEW LETTERS PRL 95, 203901 (2005), the contents of which are incorporated herein by reference. Other examples of metamaterials are described by Ulf Leonhardt, et al in “Optical Conformal Mapping” Science 312, 1777 (2006), and by Pendry et al in “Controlling Electromagnetic Fields” Science 312, 1780 (2006)), the contents of both of which are incorporated herein by reference.